Up until now it has been a wide practice as a prevention measure against looseness of a tightened screw to cover or melt a moldable material for bonding to the surface of the screw. This was economic and made the connection solid.
Examples of these measures are given below.
(1) Holes are mechanically punched in the surface of the screws and a thermoplastic resin which is used to fill up the holes.
(2) A small bit of the thermoplastic resin is pushed over the surface of the screw and a bonding portion of the thermoplastic resin is formed around the screw surface.
(3) The screw surface is heated and a thermoplastic resin powder is sprayed on the screw surface.
(4) The screw surface is chemically or mechanically treated beforehand and then a thermoplastic resin is melted onto the rough screw surface for bonding.
In all of these examples, excluding the case where the primer, mechanical, and chemical processing is completed, or in other words, the primary processing is completed before the secondary treatment of the thermoplastic resin, there are problems in the ability to stick.
Also there are problems in the processing which is required to perform the primary processing. In the aforementioned methods, the effect of the primer processing is efficient and desirable. However, because the comparatively expensive primer material must be spread over the entire screw surface it is a waste of time and material.
Moreover, there is the fear that when the primer is spread on the entire screw surface, there will be leakage in layer between the primer and the thermoplastic resin which will destroy the seal.